Prior to this invention, polysiloxanylenes containing recurring arylene backbone groups and particularly arylene backbone groups containing carbonate moieties, have not been successfully prepared in high molecular weights, viz., in molecular weights of 100,000 and above. Such arylenesiloxanylene polymers, prepared in accordance with prior art procedures, have demonstrated considerably lower molecular weights, and relatively poor physical and mechanical properties. These prior art polymers have no established practical application.
The polyarylenesiloxanylenes of the present invention are polymers having the characteristic structural formula: ##STR2## where Y is an arylene or substituted arylene moiety, preferably one which additionally contains a carbonate group; R and R' are the same or different alkyl group(s), substituted alkyl group(s) or a phenyl group, and are preferably lower alkyl or substituted lower alkyl groups containing from 1 to 3 carbon atoms; x ranges from about 1 to 3; and n ranges from 300 to 1500, said polymers having molecular weights (number average) of 100,000 and higher. This structural formula is referred to hereinafter as Formula A. The present invention permits the synthesis of highly pure arylene bis-silanol monomers and their polymerization in the presence of phosgene and an aromatic heterocyclic amine inert to reaction with phosgene, e.g., pyridine, methyl pyridine, cholidines and the like, to obtain high molecular weight homopolymers and copolymers, many of which are transparent, exhibit good adhesion to polycarbonates and glass and can withstand temperatures as high as 400.degree. F. without degradation. Characteristically, the arylene-siloxanylene polymers, including those containing organocarbonate groups, prepared in accordance with this invention, exhibit viscosities beyond one deciliter per gram (1 dl/g). Additionally, these polymers display good mechanical properties for practical applications. The polymers of this invention provide base materials for high temperature-resistant, optically-transparent elastomers suitable for use in such applications as interlayer sheet materials for the fabrication of laminated safety-glass-type aircraft windshields and canopy assemblies.
The present invention relates to the syntheses of highly purified bis-silanols, such as, bis[(4-hydroxydimethylsilyl)phenyl]carbonate, bis[4-(1-hydroxy-1,1,3,3-tetramethyldisiloxanyl)phenyl]carbonate, bis(3-hydroxydimethylsilylphenyl)carbonate, bis[3-(1-hydroxy-1,1,3,3-tetramethyldisiloxanyl)phenyl]carbonate, bis[4-(1-hydroxy-1,1,3,3-tetramethyldisloxanyl)]benzene and their polymerization with phosgene (carbonyl chloride) to form high molecular weight siloxanylene polymers.
The highly pure bis-silanols obtained in accordance with this invention are essential in the synthesis of the desired high molecular weight siloxanylene polymers. It is well known that silanols, especially in the presence of a catalytic amount of acid or base, or at a high temperature, undergo condensation reactions to form siloxanes in accordance with the following equation: EQU .tbd.Si--OH+.tbd.Si--OH.fwdarw..tbd.Si--O--Si.tbd.+HOH
Thus, in the prior preparation of arylene bis-silanols, siloxanes were usually formed. This reaction not only consumed the synthesized silanols, but the siloxane formed an oily mixture with the silanol, which mixture, in many cases could not be separated adequately. As a result of the aforementioned side reaction, many silanols which have been prepared by existing literaure methods are virtually impure compounds and tend to form only low molecular weight polysiloxanes when polymerized.
In accordance with the present invention, however, pure bis(4-hydroxydimethylsilylphenyl)carbonate and bis[4-(1-hydroxy-1,1,3,3-tetramethyldisiloxanyl)phenyl]carbonate, together with its corresponding meta analog, were prepared starting with the 3- or 4-bromophenol.
Although certain of the reactions which were utilized to prepare select monomers in accordance with a new five (or seven)-step synthesis for the production of high molecular weight, carbonate-containing, arylene siloxanylene polymers of this invention are based on reactions indicated in Lloyd, et al., U.S. Pat. No. 3,595,974 and Mironov, et al., U.S. Pat. No. 3,697,569; the procedures indicated in these Lloyd, et al., and Mironov, et al., patents were found inadequate for providing intermediates and monomers of the high purity required to obtain the high molecular weight polymers of this invention. For example, 4-dimethylsilylphenol, the preparation of which is identified herein below in the detailed description of the invention as Step 3, was reported by Mironov in U.S. Pat. No. 3,697,569 to melt at 35.degree. to 37.degree. C. However, 4-dimethylsilylphenol was isolated by the present inventors as a compound melting at 61.degree. C.
Similarly, although Lloyd, et al., U.S. Pat. No. 3,595,974 disclosed the preparation of several silylphenyl carbonate intermediates, the procedures disclosed fail to result in obtaining any pure bis[(4-hydroxydimethylsilyl)phenyl]carbonate. This is in sharp contrast with the synthesis procedure of this invention which results at each stage in a product which could be isolated in a high state of purity.
The preparation of siloxane-containing polymers containing carbonate and polysiloxy blocks has been reported in U.S. Pat. No. 2,999,845, issued to Goldberg. This Goldberg patent is directed to the preparation of such block copolymers by reacting dihydric phenols with a carbonate ester, and dimethyldichlorosilane. Although the Goldberg patent utilizes a phosgenation step in pyridine in the course of preparing the referenced Goldberg polymers for the generation of the carbonate linkages, no such reaction occurs in the present invention. It will be apparent that the specific polymerization step of this invention, using the phosgene in the presence of an aromatic heterocyclic amine inert to reaction therewith, e.g., pyridine, for obtaining the highly purified polymers, is readily distinguishable from the Goldberg patent and the other prior art mentioned herein in that the phosgene does not react to form such linkages. The block copolymers formed in accordance with this Goldberg patent contain hydrolytically unstable phenoxy-silyl bonds in the polymer backbone structure. No such bonds are present in the polymers of this invention. The Goldberg phosgenation process for polymerization uses phosgene to form carbonate linkages whereas in this invention phosgene is used to promote the formation of siloxane linkages (probably by dehydrating silanols or acting as a polymerization catalyst to promote formation of siloxane bonds).
U.S. Pat. No. 3,832,419 issued to Merritt, Jr., is directed to the preparation of organopolysiloxane-polycarbonate block copolymers from halogen chain-stopped organopolysiloxane, dihydric phenol and phosgene in a process which uses ammonia as an acid acceptor in the initial dihydric phenol/halogen chain-stopped organopolysiloxane reaction. This reaction is then followed by phosgenation to form the copolymers apparently in a manner similar to Goldberg U.S. Pat. No. 2,999,845. Nowhere does Merritt, Jr. teach preparation of polysiloxanylene arylene carbonates.